This invention relates to a method of semiconductor assisted metal deposition and article of manufacture for nanolithography applications, especially where the formation of metal patterns of high resolution is important, such as in the electronics industry. More particularly, the invention relates to a method for forming a metallic deposit in a precise pattern on a semiconductor, such as titanium dioxide, by use of a surface modifier deposited on the semiconductor. Preferably, the semiconductor is of nanoparticle size, and the modifier is selected to provide both a hole (in the electronic sense) scavenging and chelating effect. The metal is applied in the form of ions which are subsequently reduced by a photocatalytic action. Preferably, the metal is copper, silver, or gold.
The electronics industry has made considerable progress in its efforts to miniaturize electronic components for purposes of creating much smaller products for use, for improving performance and also for reducing power consumption requirements. Since the development of integrated circuits, there has been a need to reduce the size of all electronic components, including conductor interconnects, capacitors, inductors and other such components. Currently, the available technology cannot easily establish dimensions for electronic components less than about 100 nm-200 nm. Such dimensional limitations are preventing further progress in electronic device performance and general miniaturization needs.
It is therefore an object of the invention to provide an improved method and article of manufacture of ultra-fine dimensioned electronic components.
It is another object of the invention to provide a novel method and article of manufacture of ultra-fine dimensioned metallic conductor components.
It is a further object of the invention to provide an improved method and article of manufacture of nanoparticles of a semiconductor having metals deposited thereon.
It is yet another object of the invention to provide a novel method and article of manufacture of semiconductor oxide treated by a bidentate liquid to enable controlled deposition of metals on the semiconductor oxide. It is still an additional object of the invention to provide an improved method and article of manufacture of semiconductor oxide of nanoparticle size treated to create metal deposition sites activated by a source of light energy.
It is also a further object of the invention to provide a novel method and article of manufacture for reducing metal ions by photocatalytic activation to deposit metal onto a semiconductor base.
It is yet another object of the invention to provide an improved method and article of manufacture for reducing metal ions by a scanning tunneling microscope to deposit metal onto a semiconductor base.
Photocatalytic reactions on surfaces have been found to be very important in various applications, such as environmental cleanup and remediation. Examples include oxidation of organic materials and reduction of heavy metal ions in industrial waste streams. In the case of using a TiO2 material, TiO2 nanoparticles are expected to have unique surface chemistry due to their larger surface area. Photoirradiation of TiO2 nanoparticles with photo energy larger than the bandgap (3.2 eV) creates electron-hole pairs. Following irradiation, the TiO2 nanoparticles act as either electron or hole donors to reduce or oxidize materials, respectively, in the surrounding media. However, the photo-induced charge separation in bare TiO2 nanoparticles has a very short lifetime because of charge recombination. It is therefore important to prevent electron-hole recombination before a designated redox reaction occurs.
In one embodiment of the present invention the use of selected nanoparticles of semiconductors can be manipulated to control photo-induced charge separations and enhance metal ion deposition to create desirable electronic components. For example, a layer of a semiconductor, such as TiO2 in the nanoparticle size regime of about 45A, is deposited on a glass or other support. To the semiconductor component is added a modifier, such as a bidentate ligand (alanine), to provide both hole scavenging and a chelating effect in order to prevent rapid electron-hole recombination. Further, simultaneously or subsequently with adding the ligand, a source of conductive metal ions, such as copper, silver, or gold, is added to the modified surface of the titanium dioxide. The surface is activated by directing a source of light energy onto the modified surface with metal ions to reduce the metal ions to form elemental metal in the desired electronic pattern on the semiconductor base. With a general source of light energy, a mask will typically be necessary to form the desired pattern of metal. However, when a laser or a source of synchrotron X-rays used as a photon source, no mask is needed; the pattern is produced by moving the sample relative to a stationary light source by a stepper motor, for example. Preferably, the pattern is produced by using a scanning tunneling microscope (STM).
One area of potential use of the invention is in the production of miniature sized circuit elements with patterns of conductive metal of relatively high resolution. These patterns can be arranged with or without other material layers to construct many types of electronic components, such as CMOS devices. The high resolution of such patterns results from the selection of a semiconductor with a particle size in the range of 20-70 A. Such a semiconductor process is, for example, useful for producing miniature circuit elements of copper on silicon wafers or other semiconductors.
While the semiconductor oxides of the preferred embodiment differ from the silicon composition of more typical semiconductors, such as Si, it is believed that the invention provides a method of forming metal patterns of high resolution on a semiconductor base and that specific advantages of the invention for electronic products result.
Accordingly, the invention can be described as a semiconductor assisted metal deposition for nanolithography applications and resulting products, such as integrated circuit components. The semiconductor preferably is titanium dioxide, although it can include many other semiconductor materials, such as tungsten dioxide, vanadium dioxide, and doped compositions from these materials. In the method, a film of the semiconductor is formed on a substrate or glass or other conventional material. Preferably, the semiconductor is of nanosize particles with essentially uniform particle sizes in the order of 20-70 A diameter. A modifier, which is preferably bidentate ligand (alanine), is applied to titanium dioxide to provide a surface with enhanced activity as initiated by the application of light or other energy. Other modifiers can include selected compositions based on aminophosphoric acids, glycine, lucine, and the like. Simultaneously or subsequently, a source of metal ions, such as, copper, silver, or gold is applied to the modified surface of the semiconductor. A source of energy (such as light) is then applied to activate the metal ion reduction to form the desired conductive pattern. When using a conventional light source, a mask will typically be necessary to form the desired pattern. Preferably, the pattern is formed by the use of a scanning tunneling microscope (STM) which is capable of forming the pattern with high resolution. Alternatively, a laser or an X-ray beam can be used as a light source. The use of a semiconducting small particle size is important in producing the metallic patterns with fine resolution when using X-rays or STM for catalytic deposition.